1. Field of the Invention
The present invention relates to a ceramic multilayer substrate incorporating a chip-type ceramic component and a method for producing the same. More particularly, the present invention relates to a ceramic multilayer substrate and a method for producing the same in which connectivity between a chip-type ceramic component and a wiring conductor can be enhanced.
2. Description of the Related Art
As this type of technique, there is conventionally known a multilayer ceramic substrate incorporating an electronic component, which is described in Japanese Unexamined Patent Application Publication No. 63-122295. The multilayer ceramic substrate incorporating an electronic component includes a multilayer ceramic substrate, a chip-type electronic component embedded in a space constituted by a recess or a through-hole within the multilayer ceramic substrate, and a conductor interconnecting the chip-type electronic component provided between the layers or in the space of the multilayer ceramic substrate. In such a multilayer ceramic substrate, a chip-type capacitor is mounted on an internal conductor composed of a conductive paste, and the internal conductor is sintered simultaneously with sintering of the ceramic multilayer substrate to thereby connect the outer electrode of the chip-type capacitor and the internal conductor to each other.
In general, internal conductors of a ceramic multilayer substrate are composed of a metal material, such as Cu or Ag, and external electrodes of a chip-type capacitor are composed of a metal containing Ni as a main constituent in order to reduce cost. An internal conductor includes an in-plane conductor extending along the interface between upper and lower ceramic layers and having a predetermined pattern, and a via conductor electrically connecting upper and lower in-plane conductors. A chip-type capacitor is connected to an in-plane conductor and/or a via conductor serving as an electrode.
However, in the conventional ceramic multilayer substrate, in the case where Cu is used to form internal conductors, Cu is easily oxidized and it is difficult to set conditions for firing. Since the variation of firing atmosphere affects quality, the quality is not stabilized, which is a problem. In contrast, in the case where Ag is used, the problem associated with Cu does not occur. However, since Ag and Ni do not form a solid solution, there is a possibility that, in comparison with the case where Cu is used as a main constituent, internal conductors containing Ag as a main constituent in the ceramic multilayer substrate may not be sufficiently connected to external electrodes of a chip-type ceramic component, such as a chip-type capacitor, containing Ni as a main constituent. If connectivity between an internal patterned electrode and an external electrode is unsatisfactory, cracks and fractures may occur at the junction between the ceramic multilayer substrate and the chip-type ceramic component due to shrinkage stress, drop impact, or the like in the process of sintering of the ceramic multilayer substrate. This results in problems, such as degradation in electrical characteristics and mechanical characteristics.